Center PI:Deisseroth,Karl. Principal Investigator (Project 3): Malenka, Robert C. Project Summary/Abstract MDMA is a drug that has addictive liability yet at modest doses it enhances feelings of trust and empathy. These prosocial effects of MDMA contrast with the closely related and extensively abused psychostimulant methamphetamine (MA). To decrease the abuse liability of both drugs, it is critical to define the synaptic and circuit adaptations that mediate the prosocial effects of MDMA and distinguish those from the mechanisms responsible for MA?s high addictive liability. As a first step, we will combine in vivo and ex vivo approaches to define how MDMA and MA modifies the functioning of mesolimbic dopamine (DA) and dorsal raphe serotonin (DR 5-HT) circuits at doses that have distinct behavioral effects. Initially, we will establish an MDMA dose that is prosocial but not reinforcing and an MA dose that is reinforcing but not prosocial. We will then determine how chronic administration of these drugs influences their behavioral effects. Once dosing regimens are established, we will use pharmacological manipulations and a conditional knockout mouse line to define key molecular targets mediating these behavioral effects as well as their critical brain locations focusing on serotonin and DA transporters (SERT, DAT) and specific subtypes of 5-HT receptors. In a third series of experiments, we will define how acute MDMA and MA application influences synaptic transmission in D1- and D2 medium spiny neurons (MSNs) in the NAc as well as their intrinsic excitability. We will next define the input-specific adaptations at excitatory synapses on NAc MSNs as well as on VTA DA neurons caused by acute and chronic in vivo MDMA and MA administration. This will involve combining recordings from ex vivo slices and in vivo expression of optogenetic reagents (e.g. ChR2) in areas projecting to NAc or VTA and that are shown to be influenced by these drugs in Project 1. In final experiments we address two critical questions focusing on the 5-HTergic system. Does activation of DR inputs to the NAc mimic the behavioral effects of MDMA? Does endogenous activity within these identified circuits correlate with these same behaviors? To address these questions we will use molecular interventions to bidirectionally control activity in 5-HT inputs to NAc and determine the behavioral effects. To enhance understanding of these circuit elements in the context of the Center?s overall goals, we will also collaborate with the Technology core to use viral tracing techniques combined with CLARITY/COLM to define the input-output connectivity relationships of DR 5-HT neurons. Finally, we will collaborate with the Deisseroth lab and Technology core to elucidate the brainwide activity responses to DR 5-HT neuron stimulation using FIP. This extensive series of experiments will be prioritized and modified appropriately as Center results accumulate. By integrating the results from this project with those from other Center projects, we will facilitate elucidation of the circuit dynamics that mediate the prosocial versus reinforcing actions of MDMA and MA and how changes in these circuit dynamics contribute to the therapeutic and addictive liability of these drugs.